ABSTRACT Overland flow resistance of the four different types of surface roughness implemented by tillage operations were investigated. A microscopic approach was used to evaluate surface roughness and flow parameters on field plots. The surface roughness index was determined as a unit hydraulic radius using spectral analysis to define surface geometry and hydraulic concepts of the boundary layer. Flow velocity measurement techniques were developed that used floating objects and video-cameras. Hydrostatic water pressure from the tilled layer and overland flow were measured with piezometer sets installed under the plots. Three commonly used resistance coefficients; Darcy-Weisbach friction factor, f; Manning's roughness, n; and Chezy resistance factor, c, were evaluated for rill and interrill areas separately. The values of n for rill flow are generally in the range found in other studies. These values are representative of rill flow and do not reflect the resistance of interrill areas. A physical relationship was developed based on the dynamics of deformable boundaries to relate friction factor to the ratio of boundary shear Reynolds number to flow Reynolds number, degree of surface roughness inundation and degree of flow defect. This relation was found to be statistically satisfactory for the field data.